(1) Field of the Invention
The present invention relates to a rotary drive apparatus, more particularly, to a rotary drive apparatus which can be used, for example, as an actuator of a solenoid valve for controlling the idling speed of an automobile engine.
(2) Description of the Prior Art
In a conventional rotary drive apparatuses provided with a rotary proportional solenoid and a return spring, a rotor is controlled to a predetermined rotation angle defined by the electromagnetic force generated by the solenoid coil and the force of the return spring. Mechanical return springs, however, require troublesome fixing and adjustment to ensure spring linear characteristics. Also, there is a limit to the service life of the rotary drive apparatus.
To overcome this problem, there is known for example, in U.S. Ser. No. 499,402, a rotary drive apparatus which can control the rotation angle of the rotor with a high reliability by using an electromagnetic return force instead of a mechanical return spring. The apparatus has a long service life and relatively simple construction, however, still can be improved in respect to production of its components, assembly, and adjustment.